Bottom Line:
We therefore generated mice lacking both ATGL and HSL (A0H0).Markedly decreased acid TG hydrolase activity and lipid flux independent of bafilomycin A1 treatment, however, argue against effective lysosomal degradation of LDs in A0H0 macrophages.We conclude that autophagy of proteins and cell organelles but not of LDs is active as a compensatory mechanism to circumvent and balance the reduced availability of energy substrates in A0H0 macrophages.

Mentions:
Finally, we investigated whether the terminal step in autophagic lipid degradation is induced in lipase-deficient macrophages. To this extent, we first determined the protein expression of LAL, the major TG and CE hydrolase in lysosomes. As shown in Fig. 5A, LAL protein expression was comparable between macrophages from all genotypes. Lal-deficient (L0) macrophages were used as control. Acid TG hydrolase activity, which reveals the activity of the lysosomal TG hydrolase LAL, was slightly decreased in H0 and ~80% reduced in A0 and A0H0 compared to Wt macrophages (Fig. 5B). Acid CE hydrolase activity was comparable in macrophages from all genotypes (Fig. 5C). As a control, L0 macrophages showed drastically reduced acid TG and CE hydrolase activities (Fig. 5B, C). Comparable with A0H0 macrophages, L0 macrophages showed increased dequenched DQ-BSA (Fig. 5D), suggesting an elevated lysosomal proteolysis even in cells lacking the major acid hydrolase. Starvation, a known inducer of autophagy, failed to decrease intracellular TG concentrations in macrophages of all genotypes (Fig. 5E). We starved the cells for 1.5 h since a longer starvation period drives lipase-deficient cells into cell death (unpublished observation). In summary, our data suggest that although autophagy is active in macrophages lacking both ATGL and HSL, degradation of LDs by LAL is less effective.

Mentions:
Finally, we investigated whether the terminal step in autophagic lipid degradation is induced in lipase-deficient macrophages. To this extent, we first determined the protein expression of LAL, the major TG and CE hydrolase in lysosomes. As shown in Fig. 5A, LAL protein expression was comparable between macrophages from all genotypes. Lal-deficient (L0) macrophages were used as control. Acid TG hydrolase activity, which reveals the activity of the lysosomal TG hydrolase LAL, was slightly decreased in H0 and ~80% reduced in A0 and A0H0 compared to Wt macrophages (Fig. 5B). Acid CE hydrolase activity was comparable in macrophages from all genotypes (Fig. 5C). As a control, L0 macrophages showed drastically reduced acid TG and CE hydrolase activities (Fig. 5B, C). Comparable with A0H0 macrophages, L0 macrophages showed increased dequenched DQ-BSA (Fig. 5D), suggesting an elevated lysosomal proteolysis even in cells lacking the major acid hydrolase. Starvation, a known inducer of autophagy, failed to decrease intracellular TG concentrations in macrophages of all genotypes (Fig. 5E). We starved the cells for 1.5 h since a longer starvation period drives lipase-deficient cells into cell death (unpublished observation). In summary, our data suggest that although autophagy is active in macrophages lacking both ATGL and HSL, degradation of LDs by LAL is less effective.

Bottom Line:
We therefore generated mice lacking both ATGL and HSL (A0H0).Markedly decreased acid TG hydrolase activity and lipid flux independent of bafilomycin A1 treatment, however, argue against effective lysosomal degradation of LDs in A0H0 macrophages.We conclude that autophagy of proteins and cell organelles but not of LDs is active as a compensatory mechanism to circumvent and balance the reduced availability of energy substrates in A0H0 macrophages.